Refining light hydrocarbon distillates



Patented Feb. 16, 1943 UNITED STATES PATENT QFFICE REFININ G LIGHT, H YDR/OCARBON DISTILLATES No Drawing. Application November 6, 1941,

Serial No. 418,048

8 Claims.

The present invention which is a continuation in part of our application Serial No. 354,812, filed August 30, 1940, relates to an improved process for the doctor sweetening of hydrocarbon distillates and more particularly of cracked gasolines. It has for its object the production of a treated distillate which has good color and gum stability, good inhibitor susceptibility, good lead susceptibility and which suffers minimum octane number decrease in the course of the treatment, and furthermore yields a spent doctor solution which is easily capable of regeneration by standard procedures. It is a further object of our invention to carry out the doctor sweetening with a minimum amount of sulfur, and it is another object to carry out the doctor sweetening process with consistent and easily reproducible results.

The known doctor or plumbite sweetening process, wherein evil-smelling and otherwise harmful mercaptans in sour hydrocarbon distillates are converted to other less obnoxious compounds has been employed on a widespread scale for many years. This process in its essence comprises comingling a sour hydrocarbon distillate, such as gasoline, with aqueous sodium plumbite (doctor) solution. A yellow or brown coloration appears in the gasoline due to certain intermediate oil-soluble lead-compounds formed. Elemental sulfur in the form of a powder, solution or suspension in either a sweet or sour hydrocarbon distillate is added. This causes the so-called break or precipitation of a solid substance believed to be lead sulfide, whereupon th distillate turns clear and sweet.

As practiced heretofore, there have been many serious objections to the doctor sweetening process because the distillates treated thereby have sometimes poor inhibitor susceptibilities and often have greatly reduced induction periods, tane numbers and lead susceptibilities, etc. Thus the process has been subject to very erratic and inconsistent results obtained with respect to the enumerated properties of the treated gasolines, this difficulty being due to a large extent to heretofore unexplained variations in the amounts of sulfur required to bring about the break.

In the course of regenerative doctor treatment, i. e. sweetennig of sour hydrocarbon oils by treatment with sodium plumbite solutions, whereby spent plumbite solution is produced which is regenerated by oxidation, e. g. air blowing, treatment with chlorine, etc., acidic components such as naphthenic acids, alkyl phenols, etc., tend to accumulate in the plumbite solution thereby forming salts or soaps. These soaps or salts frequently interfere with proper doctor treatment, resulting in poor rate of regeneration of the spent plumbite solution, foaming during its oxidation, difficulty in separating the plumbite solutions and hydrocarbon phases, and cloudy appearance of hydrocarbon oils which is difficult to brighten. Therefore it has been common practice to pro-treat hydrocarbon oils which contain acids stronger than mercaptans with strong caustic alkali to remove as many as possible of these stronger acids together with a portion of the mercaptans prior to the doctor sweetening.

In our copending application Serial No. 354,812, we have disclosed that contrary to accepted practice it is desirable to pre-remove only the relatively stronger acids and to retain substantially all the mercaptans, together with at least a portion of the alkyl phenols in the hydrocarbon oil to be doctor treated. By so doing it was found that more stable gasoline is produced and'that frequently a faster break can be obtained than was to be had by the old method. In our copending application a method of pretreatment was described by which acids stronger than mercaptans and alkyl phenols can be removed selectively.

Now we have discovered in order that best results be obtained, 1. e. clear and stable gasolines be produced, the sour gasoline be treated with a plumbite solution containing alkyl phenols between definite narrow limits. Acids stronger than alkyl phenols, i. e. naphthenic acids, fatty acids, or other carboxylic acids, should preferably be absent.

Thus, our invention comprises carrying out a doctor treating process under conditions such that the phenol content of the alkaline plumbite treating solution is maintained at a concentration of 8-15 gr./liter, and preferably 9-12 gr./liter.

There are several methods by which this concentration can be maintained and the choice of the proper method or combination of methods depends largely on the type of hydrocarbon oil being treated. It is known that when contacting a hydrocarbon oil with an alkaline solution containing alkyl phenols, an alkyl phenol equilibrium is established between the hydrocarbon and aqueous phases, the hydrocarbon oil resulting from the contact containing an equilibrium amount of alkyl phenols. In order that the concentration of the alkyl phenols in the doctor solution remain substantially constant, it is therefore necessary to introduce continuously into the contact zone an amount of alkyl phenols equal to the equilibrium amount carried away by the contacting hydrocarbon oil.

If the gasoline to be treated naturally contains alkyl phenols in excess of the concentration which will establish the desired equilibrium concentration of 8-15 grams of alkyl phenols in the doctor solution, it is necessary to suitably pretreat the hydrocarbons with a caustic alkali to remove this excess. This may be achieved by the pretreating method described in our copending application Serial No. 354,812, which method at the same time enables substantial removal of acids stronger than alkyl phenols, provided it is accompanied by analytical controls designed to maintain the content of the alkyl phenols in the doctor solution at the exact desired level. If this content tends to rise as indicated by analyses, the pretreatment must be made more severe within the limits described in said copending application, so as to pre-remove more alkyl phenols; on the other hand, if the content tends to drop, the pretreatment must be milder or alkyl phenols must be added to the contact zone from some other source.

The required concentration of alkyl phenols in the pretreated hydrocarbon phase necessary to maintain the desired concentration of alkyl phenols in the doctor solution further depends on the strength of the doctor solution itself, i. e., its concentration of free NaOH and sodium plumbite. This factor is an additional reason for the necessity of controlling the alkyl phenols by analytical means.

The above pretreatment comprises contacting of a hydrocarbon oil containing mercaptans, alkyl phenols and stronger acids with a pre-determined amount of a relatively weak aqueous solution of an alkali metal hydroxide, which solution preferably contains substantial amounts of alkali metal alkyl phenolates.

If the pretreatment is correctly carried out, the break may be effected with a minimum amount of sulfur, i. e., an amount of sulfur not substantially in excess of or even less than the theoretical quantity required to convert the mercaptans retained in the distillate to disulfides. The many advantages resulting from effecting the break with a minimum amount of sulfur are well known. Thus, by this method of sweetening, gasolines are obtained which are free from corrosive sulfur, have reduced copper dish gum values, while at the same time reductions in octane numbers and lead susceptibilities are minimized.

After completed sweetening, the resulting doctor solution still containing 8-15 gr./liter of alkyl phenols is then withdrawn and regenerated preferably by air blowing. The regeneratedsolution is then returned for sweetening further amounts of sour hydrocarbon oils.

The following table illustrates some of the benefits to be obtained from our treatment.

Table Grams alkyl phenol per liter in doctor 10 Above solution Appearance of treated Clear Clear Cloudy.

gasoline. Timeforbreak Fast Fast Slow. Regeneration. Satisfactory, Satisfactory. Difficult.

3. In a sweetening process wherein sour hydrocarbon distillate containing alkyl phenols is treated with an aqueous alkaline plumbite solution and sulfur to produce a sweet distillate and a spent solution which is regenerated by oxidation, the improvement comprising pretreating said distillate under conditions to result in an equilibrium concentration of alkyl phenols in the treated hydrocarbon distillate corresponding to 8-15 gr. A. P./liter in the plumbite solution, and contacting the resulting pretreated distillate with said plumbite solution.

4. The process of claim 3 wherein the hydrocarbon distillate is a cracked hydrocarbon distillate.

5. The process of claim 3 wherein said pretreatment comprises contacting said hydrocarbon distillate with a weak aqueous solution of alkali metal hydroxide.

6. In an improved sweetening process wherein sour hydrocarbon distillate containing alkyl phenols is treated with an aqueous alkaline plum-bite solution and sulfur, the steps comprising pretreating said hydrocarbon distillate under conditions to'result in an equilibrium concentration of alkyl phenols in the pretreated hydrocarbon distillate corresponding to 8-15 gr. A. P./liter in the plumbite solution, treating the resulting pretreated hydrocarbon distillate with an alkaline plumbite solution containing 8-15 gr./liter of alkyl phenols, separating the resulting spent plumbite solution and regenerating it by air blowing.

'7. In a sweetening process wherein a sour .hydrocarbon distillate, containing less than the equilibrium amount of alkyl phenols corresponding to 815 grams of alkyl phenols per liter in an aqueous alkaline plumbite solution, is treated with an aqueous alkaline plumbite solution and sulfur, to produce a sweet distillate and a spent solution which is regenerated by oxidation, the improvement comprising adding sufficient alkyl phenols to said hydrocarbon distillate to produce a hydrocarbon distillate containing an alkyl phenol concentration which is in equilibrium with 8-15 grams of alkyl phenols per liter in said aqueous alkaline plumbite solution, and then treating the resulting hydrocarbon distillate with said aqueous alkaline plumbite solution containing 8-15 gramsof alkyl phenols per liter.

8. In a sweetening process wherein a sour cracked hydrocarbon distillate, containing more than the equilibrium amount of alkyl phenols corresponding to 8-15 grams of alkyl phenols per liter in an aqueous alkaline plumbite solution, is treated with an aqueous alkaline plumbite solution and sulfur, to produce a sweet distillate and a spent solution which is regenerated by oxidation, the improvement comprising reducing the alkyl phenol concentration in said hydrocarbon distillate sufficiently to produce a hydrocarbon distillate containing an alkyl phenol concentration which is in equilibrium with 8-15 grams of alkyl phenols per liter in said aqueous alkaline plumbite solution, and then treating the resulting hydrocarbon distillate with said aqueous alkaline plumbite solution containing 8-15 grams of alkyl phenols per liter.

PAUL V. BROWER LOWREY LOVE. 

